ABOARD AIR FORCE ONE (Reuters) - President Donald Trump is not moving to fire U.S. Special Counsel Robert Mueller but is frustrated by the length of the ongoing probe into Russian meddling in the 2016 U.S. election, the White House said on Monday.

Fayez Nureldine/GettyAs Saudi Arabia's crown prince arrives in Washington for a diplomatic trip that doubles as confirmation of his geopolitical emergence, his U.S.-backed prosecution of a devastating war in Yemen may prove a stumbling block.

If things break the way three senators seek, then as early as Tuesday, the Senate will debate and then vote on ending U.S. military refueling, targeting analysis and other assistance to the Saudi war on Houthi-controlled Yemen. That war, for the past three years, has featured indiscriminate civilian bombing and facilitated a mass famine and cholera outbreak. And its primary mover is the Saudi defense minister and heir apparent, Mohammed bin Salman, ubiquitously known as MBS, who is slated to meet with President Trump at the White House on Tuesday.

It's been a long procedural road for a resolution pushed by independent Bernie Sanders, Democrat Chris Murphy, and Republican Mike Lee to end aid for the Yemen war. Their resolution, introduced in the Senate foreign relations committee on March 1 and therefore ripe for a move to the floor, holds U.S. assistance in that war in violation of the 1973 War Powers Resolution. The resolut